Make sure that your device, Apple, and iTunes can communicate

If you see error 1671, iTunes is downloading necessary software. Wait for the download to finish, then try again. To see how long the download should take, click the down arrow in the upper-right corner of iTunes.

If you see one of the errors below, your computer might not be able to connect to Apple servers or your iPhone, iPad, or iPod touch:

If you see error 4037, iTunes is unable to update your iOS device because it's passcode locked and the device wasn't unlocked for the update or restore. Unlock your device and try again. Learn what to do if you forgot your passcode.

Check for outdated or modified software

If you see error 1015 or a message that "the required resource can't be found," your device might have unauthorized iOS modifications (jailbreaking). Or you might be trying to install an earlier version of iOS (downgrading).